A H₂ -oxidizing, 1,2,3-trichlorobenzene-reducing multienzyme complex isolated from the obligately...

Dehalococcoides mccartyi is a small, slow-growing bacterium of the phylum Chloroflexi that conserves energy using aliphatic and aromatic organohalides as electron acceptors, and hydrogen as sole electron donor. A recent study identified a protein complex in the membrane of strain CBDB1 comprising a Hup hydrogenase, a complex iron-sulphur molybdoprotein and a reductive dehalogenase (RdhA) that catalyses reduction of 1,2,3,4-tetrachlorobenzene. Using a combination of size-exclusion chromatography, in-gel hydrogenase activity-staining, immunological analysis and mass spectrometry, we identified here a large molecular mass protein complex solubilized from the cytoplasmic membrane of D. mccartyi strain CBDB1 that catalysed H₂ -dependent reduction of 1,2,3-trichlorobenzene (1,2,3-TCB) to 1,3-DCB. In-gel zymographic staining revealed H₂ :benzyl viologen oxidoreductase activity associated with the complex and immunological analysis identified co-elution of CdbdA195, the predicted catalytic subunit of the iron-sulphur molybdoenzyme, the chlorobenzene-specific RdhA, CbrA, and traces of HupL, the catalytic subunit of the Hup hydrogenase. Quantitative reverse transcriptase PCR analyses indicated that the expression of the hupL and cbdbA195 genes was induced by 1,2,3-TCB but not by hydrogen. Together, these data identify and describe a protein-based electron-transfer complex catalysing H₂ oxidation coupled to chlorobenzene reduction.